Corona treating apparatus having an electrode with an adjustable width



D 3 1968 J. T. DELANEY, JR 3,

CORONA TREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTHFiled May 3. 1966 Sheet of 2 Dec. 31, 1968 J- T. DELANEY, JR 3,419,489

CORONA TREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTHFiled May 5. 1966 Sheet 2 of 2 FIG.3

FIG. 2

FIG. 4

\ I i i l i i I l I i i i i United States Patent 3 419,489 CORONATREATING APPARATUS HAVING AN ELECTRODE WITH AN ADJUSTABLE WIDTH John T.Delaney, Jr., Pattenburg, N.J., assignor to Ethyl Corporation, New York,N.Y., a corporation of Virginia Filed May 3, 1966, Ser. No. 547,287 6Claims. (Cl. 204312) This invention relates to an apparatus for treatingplastic materials that are in sheet or film form. More particularly,this invention relates to an adjustable length treater electrodeassembly for use in an apparatus for treating plastic film by means ofan electrical effect produced by the passage of electrical energybetween two spaced-apart electrodes.

Untreated surfaces of certain plastic materials, e.g. polyethylene,cannot normally be satisfactorily imprinted with inks or adhesives usingconventional techniques unless the surfaces are treated prior toapplication of the ink or adhesive. The preferred present day method oftreating the surface of a plastic material to enhance its receptivity toprinting inks or adhesives is to expose the surface to an electricaleffect produced by the passage of electrical energy between spaced-apartelectrodes. The most common treating apparatus utilizes a highfrequency, high voltage discharge between the electrodes to produce aCorona or glow discharge. The apparatus commonly in use today includes arotatable cylindrical electrode which is usually connected to the groundlead of the electrical power supply. The other lead from the electricalpower supply is usually connected to a high voltage electrode whichcustomarily has the form of a relatively narrow or knife edgelongitudinal bar fixedly positioned parallel to and spaced a shortdistance from the rotating grounded electrode. An exemplary barelectrode is described in US. Patents 2,882,412 and 2,935,418.

The shape of the upper electrode has a great efiect upon the efiiciencywith which the film surface is treated, upon the amount of powerconsumption in treating the film, and upon the maintenance required tokeep a treating apparatus in operative condition. Most electricaltreating apparatuses have the film in contact with the rotatablecylindrical electrode. It has been found that for most satisfactoryservice the grounded rotatable cylindrical electrode will be providedwith a coating of a dielectric material on its cylindrical surface.Various thermoplastic materials have been used for the dielectriccoating such as polyvinyl chloride, and the polyester film sold underthe tradename Mylar. Also, these electrodes have been coated with glassby sintering directly onto the cylindrical surface. A preferred materialin common use for forming the dielectric coating is Hypalon, achlorosulfonated polyethylene.

A problem encountered in electrical treating of plastic film has beenthe damage caused to the dielectric coating on the large cylindricalelectrode by arcing between the ends of the bar electrode and therotating cylindrical electrode outside the area covered by the sheet ofplastic material which is being treated on the rotating cylindricalelectrode. When using a bar electrode that is wider than the film beingtreated, the electrical discharge between the bar and cylindricalelectrode is more intense at the end portions of the cylindricalelectrode which are not covered by the film being treated. Initially,the film receives sufficient treatment when the Hypalon covering on thecylindrical electrode is relatively new and still in good condition.However, when the heavy electrical discharge continues for some time atthe end portions of the electrodes, the Hypalon covering on the ends ofthe cylindrical electrode undergoes a deterioration from the heavyelectrical discharge and as a result loses its insulating properties.

This causes a further increase in the flow of electrical energy at theend portions of the electrodes which decreases the electrical treatmentof the film. The flow of electrical energy to the ends of the electrodescontinues to build up until arcing occurs, i.e. until substantially theentire flow of electrical energy occurs outside the area of the cylindercovered by the film being treated. Sometime the electrical resistance ofthe Hypalon fails suddenly and then all of the flow of electrical energyoccurs in the end area of the electrodes outside of that covered by thefilm being treated. This is commonly known as burn-out and when itoccurs the machine operator must shut down the treating line and havethe Hypalon covering on the cylindrical electrode replaced. To minimizethis damage, one alternative has been to cover the exposed area, i.e.that area on each end of the electrode which is not covered by the filmbeing treated, of the cylindrical electrode with additional dielectricmaterial such as plastic impregnated glass cloth, sheets of Mylar film,etc. The other altemative used in preventing this damage has been tochange the high voltage bar electrode each time the width of film beingrun through the treater is changed. This is done in order to keep thehigh voltage or treater bar electrode of a length equal to or slightlyless than the width of the film being run through the treatingapparatus. Since the spacing between the high voltage bar electrode andthe rotating grounded cylindrical electrode is critical, much time hadto be spent in adjusting the new electrode when it was replaced.Additionally, the down time caused by changing and adjusting the barelectrode resulted in a substantial loss of production of film in thosecases where the treating apparatus was used to treat the film as it Wasproduced by an extruder. Thus, there has been a need in the filmtreatingart for an adjustable length electrode which could be readily adjustedto provide for effective treatment of a number of different width filmson an electrical filmtreating apparatus without the necessity ofreplacing the high voltage electrode.

Therefore, it is an object of the present invention to provide animproved electrode assembly for a film-treating apparatus whichelectrode can be adjusted in length to accommodate a wide variety ofplastic films having different widths.

Another object of the present invention is to provide an apparatus whichemploys an adjustable electrode which can be economically fabricatedfrom readily available materials.

Still another object of the present invention is to provide an apparatusembodying an adjustable electrode assembly which will effectively treatplastic material without damaging portions of the treating apparatus.

These and other objects of the present invention are accomplished, ingeneral, in an electrode assembly which includes a central tubularmember that is provided with, at least on a part of its exteriorsurface, a plurality of substantially transverse ridges. An end tubularmember is slidably mated with each end portion of the central tubularmember, the end tubular members being provided with, at least on a partof their exterior surfaces, a plurality of substantially transverseridges.

In one embodiment of the present invention, the ridges on the centraltubular member are provided by helical threads which are formed in theexterior surface of the member. The ridges on the end tubular membersare pro vided by a helical spring carried by each one of the end tubularmembers.

In another embodiment of the present invention, the ridges on thecentral tubular member are provided by a helical spring carried by thismember and the ridges on the end tubular members are provided by helicalthreads formed in the exterior surface of each of the end members.

The foregoing and other objects of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is an elevational perspective view of a film-treating apparatusincluding the adjustable length electrode assembly of the presentinvention;

FIG. 2 is an elevational view of one embodiment for the adjustablelength electrode assembly of the present invention, with portions brokenaway to more clearly show the construction;

FIG. 3 is a view along the line 3-3 of the electrode assembly shown inFIG. 2;

FIG. 4 is an elevational view of another embodiment of the adjustablelength electrode assembly of the present invention, with portions brokenaway to more clearly show the construction; and

FIG. 5 is an elevational perspective view of a portion of a metal helixsuitable for use in the construction of the adjustable length treaterelectrode assembly.

Referring now to FIG. 1, the apparatus for treating plastic film,designated generally by the numeral 10, is adapted to electrically treata sheet of plastic material 11, which may be polyethylene,polypropylene, or any other plastic material which it is desired totreat in order to change the surface characteristics so as to improvethe adhesion of inks, adhesives and the like to its surface. Whilereference is made to a sheet of film, the film may be in the form of athin wall flattened tube as it is drawn from the nip rolls of aconventional tubular die blown film extrusion assembly. Also, the filmmay be fed from a preformed roll. The film passes over a rotatablymounted cylindrical electrode 12 which is carried on shafts 13-13,received in openings provided in spaced-apart support members 14-14.Electrical contact finger 15 presses on one end of shaft 13 and hasconnected thereto electrical lead 16 which in turn leads to the groundedside of an electrical power supply for energizing the treating apparatus (not shown).

Preferably, the cylindrical rotatable electrode 12 is covered With adielectric material such as polyvinyl chloride, the polyester film soldunder the tradename Mylar, or Hypalon, a chlorosulfonated polyethyleneor other suitable high dielectric material.

A top cross-support member 17 is attached to the upper ends of verticalsupport members 14 and extends therebetween. The adjustable lengthelectrode assembly, designated generally by the numeral 18, is suspendedfrom the top cross member 17 by means of threaded bolts 19-19 attachedthereto. The electrical lead 20 is connected to one of the bolts 19 andin turn connected to the high voltage side of the power supply (notshown). If desired, the top cross-support member 17 may be made from ahigh dielectric material such as plastic, i.e. Plexiglas, Bakelite orother good electrical insulating plastic material, or optionally thebolts 1919 may be insulated by means of suitable insulating washers andsleeves (not shown) when it is desired to make top cross member 17 frommetal or other conducting material.

Referring now to FIG. 2 of the drawings, one embodiment of theadjustable length electrode 18 of the present invention utilizes acentral portion composed of a tubular member 21. This tubular member hasa plurality of substantially transverse ridges 22 provided on theexterior surface thereof. While these ridges 22 may be formed byproviding annular grooves in the exterior surface of central member 21,a more convenient way of preparing the ridges 22 is by providing apattern of spiral ridges in the surface of the central member bythreading the exterior surface of tube 21 with a common pipe threadingapparatus. In such case the ridges 22 are helical in pattern and extendfrom one end of central member 21 to the other end thereof. It has beenfound that provision of uniformly spaced ridges 21, either in the formof annular rings or a helix, provide uniform distribution of theelectrical discharge between the adjustable length electrode 18 and therotatable cylindrical electrode 12. Projecting from the upper surface ofcentral tubular member 21 are two mounting bolts 19-19. These bolts areattached to tubular member 21 by means of nuts 23 which are welded tothe upper surface of central tubular member 21.

As can be seen more clearly in FIG. 3, each end of central tubularmember 21 is provided with a slot 24 therein. A rectangular lug 25 isWelded to central tubular member 21 immediately adjacent to the slot 24in each end thereof. Each lug has a threaded opening 26 therein whichreceives thumb screw 27. By means of the foregoing arrangement, theinside diameter of the portions of tubular member 21 can be changed tofixedly position the adjustable end tubular members 2828.

An end tubular member 28 is slidably received inside each end of centraltubular member 21. By means of the lugs 2525 and thumb screw 27 in eachend of tubular member 21, the end tubular members 28 can be locked inposition with respect to a central tube 21. The outer end of eachtubular member 29 has an arcuate shaped surface 29 which permits easyplacement of a helical spring 30 carried by each end tubular member 28.One end of the spring 30 is clamped to the end of tube 28 by means of aclamp 31. The other end is attached by a similar clamp 31 to the end ofcentral tubular member 21. Thus, as end tube 28 is slid in or out ofcentral tube 21 the spring 30 contracts or expands to distribute itselfuniformly over the surface of tube 28. By loosening thumb screw 27, tube28 may be pushed into central tubular member 21 or extended therefrom aconsiderable distance. This provides a wide range of length adjustmentfor each end of central tubular member 21 whereby the electrode may bequickly changed to accommodate any width of film passing through anexemplary film-treating apparatus as depicted in FIG. 1. The tubularsections 21 and 28 can be constructed of any suitable metal conductorsuch as aluminum or brass.

Referring now to FIG. 5, a perspective view of the metal helical spring30 is depicted. In the form of the spring depicted, the cross-sectionalshape of the helix or coil is in the form of a rectangle. In thepreferred form of the helical spring 30, all of the coils are inface-to-faoe contact with each other when the spring is under notension, i.e. a tension Spring is preferred as opposed to a compressionspring which has its helical coils separated in a n-o-load position.While the particular form of the helical spring depicted in FIG. 5utilizes a rectangular cross-sectional area, the invention is notlimited to the use of any particular shape for the spring. Coil springshaving a cylindrical cross-sectional area are also suitable for use inthe adjustable electrode of the present invention. Other forms such asellipsoidal, triangular, etc. may be used.

Referring now to FIG. 4, a second embodiment of the adjustable lengthtreater electrode assembly of the present invention is depicted. Thissecond embodiment is designated generally by the reference numeral 32.This form of the invention utilizes a central tubular portion 33 havinga smooth exterior surface and with a diameter such that it is slidablyreceived within the interior of end tubular members 34-34. The portionof the central tubular section 33 extending within the inner ends of theend tubular members 34 34 is covered by a helical spring 35. This springmay have a construction identical with that described previously for thehelical spring 30. The ends of spring 35 are attached by clips 36 to theinner ends of the end tubular members 3434. The inner end of each endtubular member 34 is slotted and provided with lugs 25 in the samemanner as shown in FIG. 3 of the drawing for the other embodiment of theadjustable length electrode. Thus, each end tube 34 can be fixedlypositioned and locked to the central tubular member 33 to provide anadjustable length electrode of wide length variation. Each end oftubular member 34 is provided with a plurality of transverse ridges 37similar to those provided in the central member 21 of the embodimentshown in FIG. 2. These ridges may be produced in similar fashion tothose of the embodiment shown in FIG. 2, i.e. they may be made byproviding annular grooves in the end members 34 or by threading eachmember throughout its length.

It is important that the outside diameter of the threaded members,whether they be end members or central members, be substantially equalto the outside diameter of the helical spring 30 or 35 used in eitherembodiment of the invention. It is essential that the ridges orprotuberances of the adjustable electrode, Whether they be provided byhelical spring or by screw threads on a particular member be of the sameoutside diameter to provide a uniform outside diameter overall for theadjustable length electrode. This is necessary in order to maintain thesame spacing of the adjustable electrode from the rotating electrodethroughout the length of the two assemblies.

In one specific embodiment of the adjustable length electrodeconstructed in accordance with the present invention as shown in theembodiment depicted in FIG. 2 of the drawings, a drawn aluminum tubinghaving a length of 18 inches and an outside diameter of 2.250 inches anda Wall thickness of 0.18 inch was used for the central tubular section.This central section was threaded throughout its length on the exteriorsurface using a standard American pipe thread die which provided eleventhreads per inch of length of the tube. The end tubular sections eachhad a length of 13 inches and were made from drawn aluminum tubinghaving an outside diameter of 1.875 inches with a wall thickness of0.058. The helical springs utilized had one hundred turns in each coil.With the end tube members extended their practical maximum length, theoverall length of the treating electrode was a maximum of 40 inches.With the end tubular members inserted as far into the central tube aspermitted by the compression of the springs carried by the end members,the adjustable length electrode had a minimum length of 26% inches.Thus, using this embodiment of the adjustable length electrode of thepresent invention, one could treat film having a width of from 26%inches to 40 inches without removing the electrode from the treatingapparatus. Additionally, the use of the present electrode avoids havingto reset the spacing between the electrode and the lower roll as occurswhen one uses a separate electrode for each width of film.

In another embodiment constructed similarly to that describedheretofore, the lengths of the various members were proportionatelyincreased but the same diameter tubing and thread size were used for thesecond embodiment. The helical springs utilized had four hundred andfifty turns in each coil. The second embodiment made according to thepresent invention had a maximum extendable length of 158 inches and aminimum length when the end sections were fully compressed of 96%inches. Thus, this form of the adjustable length electrode could treatany film having a width from 96% inches up to a maximum film width of158 inches.

From the foregoing description of the invention, it will be obvious topersons skilled in the art to make modifications thereto. Othermodifications are included in the scope and spirit of the presentinvention as defined by the appended claims.

What is claimed is:

1. In an apparatus for treating a polymeric film in a corona discharge,said apparatus comprising a first electrode and means for supporting thepolymeric film adjacent said first electrode, said means including asecond electrode and a dielectric material covering said secondelectrode, and means for supplying an electrical current to saidelectrode, the improvement wherein said first electrode comprises:

(a) a central tubular member being provided with, at least on a part ofits exterior surface, a plurality of substantially transverse ridges;and

(b) at least one end tubular member slidably mated with at least one endportion of said central tubular member, said end tubular member beingprovided with, at least on a part of its exterior surface, a pluralityof substantially transverse ridges.

2. In an apparatus for treating a polymeric film in a corona discharge,said apparatus comprising a first electrode and means for supporting thepolymeric film adjacent said first electrode, said means including asecond electrode and a dielectric material covering said secondelectrode, and means for supplying an electrical current to saidelectrodes, the improvement wherein said first electrode comprises:

(a) a central tubular member being provided with, at least on a part ofits exterior surface, a plurality of substantially transverse ridges;

(b) an end tubular member slidably mated with each end portion of saidcentral tubular member, said end tubular members being provided with, atleast on a part of their exterior surfaces, a plurality of substantiallytransverse ridges.

3. In the apparatus of claim 2 wherein said ridges on said centraltubular member are provided by helical threads formed in the exteriorsurface of said member, and said ridges on said end tubular members areprovided by a helical spring carried by each of said end members.

4. In the apparatus of claim 2 wherein said ridges on said centraltubular member are provided by a helical spring carried by said centraltubular member, and said ridges on said end tubular members are providedby helical threads formed in the exterior surface of each of said endmembers.

5. In the apparatus of claim 2 wherein means is provided to fixedlyposition each of said end tubular members on said central tubularmember.

6. In the apparatus of claim 2 wherein means is provided to mount saidelectrode in a fixed position relative to a second electrode.

References Cited UNITED STATES PATENTS 3,174,748 3/1965 Roberts et al.271--8 3,291,711 12/1966 Moyer 204-l 3,294,971 12/1966 Von der Heide25049.5

FOREIGN PATENTS 1,004,230 11/1951 France.

ROBERT K. MIHALEK, Primary Examiner.

6. IN THE APPARATUS OF CLAIM 2 WHEREIN MEANS IS PROVIDED TO MOUNT SAIDELECTRODE IN A FIXED POSITION RELATIVE TO A SECOND ELECTRODE.